1. Field of the Invention
The invention relates to vehicular anti-theft security systems that perform theft preventing operations so as to prevent or deter unauthorized use or theft of vehicles. The invention also relates to vehicular anti-theft security systems that change conditions for generating an alarm based on the expansion or contraction of suspensions and the angle of inclination of the vehicle.
2. Description of Related Art
An anti-theft security system for a vehicle is known which assumes towing or other event(s) associated with vehicle or tire theft when detecting an inclination of the vehicle, and generate an alarm based on the assumption. However, the anti-theft security system of this type may undesirably perform a warning operation upon detection of oscillation or other movement(s) of the vehicle when it is parked in, for example, a multi-level parking garage. In view of this situation, a theft detection system for a vehicle, such as that disclosed in Japanese Laid-open Patent Publication No. 2003-34233, has been proposed which performs a warning operation in a normal parking mode when an inclination sensor detect an inclination of the vehicle, but determines whether or not to perform a warning operation without taking account of the information (i.e., inclination of the vehicle) from the inclination sensor when a multi-level parking mode is set by the user upon parking in a multi-level parking garage. Thus, the inclination sensor is prevented from erroneously detecting inclination of the vehicle due to oscillation or other movement(s) thereof during entry or release of the vehicle into or from the multi-level parking garage.
According to the disclosure or suggestion of the above-identified publication, however, the theft detection system requires the user to manually operate a remote controller so as to switch to or select the multi-level parking mode for ignoring detection of inclination by the inclination sensor. Thus, the user may find it inconvenient to manually select the multi-level parking mode each time the vehicle enters or leaves the multi-level parking garage.
The above-described known anti-theft security system, which generates an alarm based on the information from the inclination sensor and others for prevention of vehicle theft, may also be actuated by mistake due to inclination of the parking place when the vehicle is parked on a slope, or in a ferry traveling on the sea, or in a multi-level parking garage. Also, a conventional anti-theft security system using a vibration sensor may be actuated by mistake due to vibrations caused by, for example, heavy rain, strong wind, or passage of heavy equipment nearby.
In view of the above situations, a vehicular anti-theft security system as disclosed in Japanese Laid-open Patent Publication No. 63-078848 has been proposed which monitors the stroke position of a shock absorber in a suspension system, and actuates a theft prevention mechanism when a substantially full stroke of the shock absorber is detected, to thereby prevent or deter theft of the vehicle while preventing erroneous actuation of the mechanism due to the inclination or vibrations as described above.
However, the anti-theft security system as disclosed in JP-A-63-078848 has the following problem: since the theft prevention mechanism is not actuated until the vehicle is lifted up and the shock absorber is placed in a substantially full-stroke condition, the security system cannot be applied to vehicles that may be jacked up and towed without having the shock absorber placed in a substantially full-stroke condition, for example, to a vehicle equipped with a vehicle-height adjustment type suspension system capable of adjusting the height of the vehicle.